Integrated circuits are often manufactured on a semiconductor substrate, such as a silicon wafer. The silicon wafer is typically a thin circular plate of silicon that is 150, 200 or 300 millimeters in diameter and approximately 25 mils thick. A single wafer will have numerous devices which are integrated circuits and are imprinted on the wafer comprising a lattice of devices. Each device consists of numerous layers of circuitry and a collection of bonding pads. The bonding pads are small sites, typically 3 mils square, made usually with aluminum (or other conductive material) that eventually serves as the device's connections to the pin leads. Other than the bonding pads, the remainder of the wafer is coated with a final layer of an insulating material such as silicon nitride, called the passivation layer, which in many respects behaves like glass. The aluminum itself forms a thin non-conductive layer of aluminum oxide, which must be eliminated or broken through before good electrical contact can be made.
Since the packaging of a device is somewhat expensive, it is desirable to test a device before packaging to avoid packaging bad devices. This process of testing devices before packaging is referred to as the sort process. This process involves connecting a device called a probe card to a special tester. The probe card has a collection of electrical contacts or pins (also referred to as probe elements) that stands in for the normal pins and wire leads of a packaged device. The wafer is then positioned so that the contacts or pins on the probe card make contact with a given device's bonding pads and the tester runs a battery of electrical tests on the device. A special machine, called a wafer prober, is used to position each device on the wafer with respect to the probe card. High accuracy is required, because the bonding pads are small and if a probe card pin makes contact outside the bonding pad area, the result may be a break in the passivation layer, which generally results in a damaged device. Also, the card pins need to be cleaned to ensure accuracy of such contact.
A primary purpose of wafer probing is to accurately position the collection of devices, or dice, on a wafer in such a manner so that the device's bonding pads make good electrical contact with a probe card's probe pins so that the device may be properly tested before dicing and packaging. Inaccuracy positioning may cause damages to either the probe pins or the bonding pads, and/or other components of the probe card and the devices on the substrate.
Types of damages that may occur include gouging of the bonding pads so as to expose the metal layer underneath and cracking of the pads thereby damaging the active components below. Other damages include damages to the probe pins such as bending and breaking. To avoid damages such as damages to the bonding pads, the motions of the probe system are controlled so as to achieve a “softer” (e.g., slower and less forceful) contact between the probe pins and the bonding pads. In one current method, the substrate is moved up to a specific height of contact, stopped, and the motion of moving the substrate is changed. The motion is slowed down so that the substrate can be moved closer to the probe pins with a reduced motion. In that way, the contact between the bonding pads and the probe pins is softer or slower. Such change of motion substantially impacts the probe system's throughput.
It is desirable to provide a probe card cleaning device and method, which overcomes the above limitations and drawbacks of the conventional testing devices.